This is added in 10.11, so we add a #define when building against older SDKs.
The decoder actually supports 7.1-channel eac3, but since the parser only
reports 6 channels, we end up decoding the 5.1 downmix (same as the internal
decoder) for now.
- ADTS-formatted AAC didn't work
- Channel layouts were never exported
- Channel mappings were incorrect beyond stereo
- Channel counts weren't updated after packets were decoded
- Timestamps were exported incorrectly